Description: Objective— Antibodies against human neutrophil antigen-3a (HNA-3a) located on choline transporter-like protein 2 induce severe transfusion-related acute lung injury (TRALI). This study aims to identify the mechanism implicated in anti–HNA-3a-mediated TRALI. Approach and Results— Our analysis shows that anti–HNA-3a recognizes 2 choline transporter-like protein 2 isoforms (P1 and P2) on human microvascular endothelial cells from lung blood vessels but reacts only with the P1 isoform on neutrophils. Direct treatment of HNA-3a–positive endothelial cells with anti–HNA-3a, but not with anti–HNA-3b, leads to reactive oxygen species production, increased albumin influx, and decreased endothelial resistance associated with the formation of actin stress filaments and loosening of junctional vascular endothelium-cadherin. In a novel in vivo mouse model, TRALI was documented by significant increase in lung water content, albumin concentration, and neutrophil numbers in the bronchoalveolar lavage on injection of human anti–HNA-3a in lipopolysaccharides-treated, as well as nontreated mice. Interestingly, although neutrophil depletion alleviated severity of lung injury, it failed to prevent TRALI in this model. Infusion of anti–HNA-3a F(ab') 2 fragments caused moderate TRALI. Finally, mice lacking nicotinamide adenine dinucleotide phosphate oxidase (NOX2 y/ - ) were protected from anti–HNA-3a-mediated TRALI. Conclusions— These data demonstrate the initiation of endothelial barrier dysfunction in vitro and in vivo by direct binding of anti–HNA-3a on endothelial cells. It seems, however, that the presence of neutrophils aggravates barrier dysfunction. This novel mechanism of TRALI primarily mediated by endothelial cell dysfunction via choline transporter-like protein 2 may help to define new treatment strategies to decrease TRALI-related mortality.

Description: Objective— Fetal/neonatal alloimmune thrombocytopenia is a severe bleeding disorder, which can result in intracranial hemorrhage (ICH), leading to death or neurological sequelae. In whites, maternal anti–human platelet antigen-1a (HPA-1a) antibodies are responsible for the majority of cases. No predictive factors for ICH are available to guide prophylactic treatment during pregnancy. In this study, we investigated antibodies from mothers with ICH-positive fetal/neonatal alloimmune thrombocytopenia and with ICH-negative fetal/neonatal alloimmune thrombocytopenia to identify serological and functional differences between the groups. Approach and Results— In an antigen capture assay, we observed a stronger binding of +ICH antibodies to endothelial cell (EC)–derived αvβ3. By absorption experiments, we subsequently identified anti–HPA-1a antibodies of anti-αvβ3 specificity in the +ICH but not in the –ICH cohort. Only the anti–αvβ3 subtype, but not the anti–β3 subtype, induced EC apoptosis of HPA-1a–positive ECs by caspase-3/7 activation, and mediated by reactive oxygen species. In addition, only the anti–αvβ3 subtype, but not the anti-β3 subtype, interfered with EC adhesion to vitronectin and with EC tube formation. Conclusions— We conclude that the composition of the anti–HPA-1a antibody subtype(s) of the mother may determine whether ICH occurs. Analysis of anti–HPA-1a antibodies of the anti–αvβ3 subtype in maternal serum has potential in the diagnostic prediction of ICH development and may allow for modification of prophylactic treatment in fetal/neonatal alloimmune thrombocytopenia.

Description: Background— In patients with acute pulmonary embolism, systemic thrombolysis improves right ventricular (RV) dilatation, is associated with major bleeding, and is withheld in many patients at risk. This multicenter randomized, controlled trial investigated whether ultrasound-assisted catheter-directed thrombolysis (USAT) is superior to anticoagulation alone in the reversal of RV dilatation in intermediate-risk patients. Methods and Results— Fifty-nine patients (63±14 years) with acute main or lower lobe pulmonary embolism and echocardiographic RV to left ventricular dimension (RV/LV) ratio ≥1.0 were randomized to receive unfractionated heparin and an USAT regimen of 10 to 20 mg recombinant tissue plasminogen activator over 15 hours (n=30; USAT group) or unfractionated heparin alone (n=29; heparin group). Primary outcome was the difference in the RV/LV ratio from baseline to 24 hours. Safety outcomes included death, major and minor bleeding, and recurrent venous thromboembolism at 90 days. In the USAT group, the mean RV/LV ratio was reduced from 1.28±0.19 at baseline to 0.99±0.17 at 24 hours ( P 〈0.001); in the heparin group, mean RV/LV ratios were 1.20±0.14 and 1.17±0.20, respectively ( P =0.31). The mean decrease in RV/LV ratio from baseline to 24 hours was 0.30±0.20 versus 0.03±0.16 ( P 〈0.001), respectively. At 90 days, there was 1 death (in the heparin group), no major bleeding, 4 minor bleeding episodes (3 in the USAT group and 1 in the heparin group; P =0.61), and no recurrent venous thromboembolism. Conclusions— In patients with pulmonary embolism at intermediate risk, a standardized USAT regimen was superior to anticoagulation with heparin alone in reversing RV dilatation at 24 hours, without an increase in bleeding complications. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT01166997.

Description: Objective— In contrast to other antibodies involved in transfusion-related acute lung injury, anti–HNA-3a antibodies are incapable of inducing direct neutrophil activation and seem to interact with endothelial cells (ECs) primarily. In animal studies, anti–HNA-3a-mediated transfusion-related acute lung injury could be precipitated in the absence of neutrophils, but was stronger when neutrophils were present. In a different context the target protein of these antibodies, choline transporter-like protein-2 (CTL-2), was reported to interact with a protein of the inner ear carrying 2 von Willebrand factor (VWF) A-domains. These observations prompted us to investigate whether VWF might be involved in anti–HNA-3a-mediated neutrophil activation, and whether signaling via CD11b/CD18 is involved, as in various other experimental settings. Approach and Results— Cell adhesion demonstrated specific binding of CTL-2 to VWF. Immunoprecipitation analysis of CTL-2/CD11b/CD18 coexpressing cells indicated that anti–HNA-3a colocalizes CTL-2 and CD11b/CD18 when VWF is present. Functional studies revealed that anti–HNA-3a-mediated neutrophil agglutination is an active, protein kinase C-dependent and partially Fc-dependent process. Agglutination and the production of reactive oxygen species seem to require the formation of a trimolecular complex between the target antigen (CTL-2), CD11b/CD18 and VWF. In line with these observations, anti–HNA-3a induced less severe transfusion-related acute lung injury and less neutrophil recruitment to the alveolar space in VWF knockout mice. Conclusions— We introduce CTL-2 as a new binding partner for VWF. Interaction of neutrophils with VWF via CTL-2 allows anti–HNA-3a to induce signal transduction via CD11b/CD18, which leads to neutrophil activation and agglutination. In transfusion-related acute lung injury, this mechanism may further aggravate endothelial leakage.